All posts tagged AOVPN

I’m commonly asked “can Windows Server with Routing and Remote Access Service (RRAS) be configured with a single network interface?” This is likely because the official Microsoft documentation references only a multihomed dual NIC configuration, leading many to believe it is a strict requirement.

Single NIC

Deploying Windows Server RRAS with a single network interface is indeed supported and works without issue. There are no functional limitations imposed by using a single network interface. All features are fully supported in this scenario. The choice to use one or two network interfaces is purely a design choice, driven by several factors such as current network configuration and security requirements.

Dual NIC

Although a single NIC configuration is fully supported, there are some important advantages associated with mulithome dual NIC deployments. The following should be considered when deciding between single NIC and dual NIC VPN configurations.

Traffic Segmentation

Having separate internal and external network connections provides logical and physical separation of trusted and untrusted network traffic. Terminating connections from Always On VPN clients on the Internet in an isolated perimeter or DMZ network yields positive security benefits.

Firewall Configuration

Using two network interfaces allows for a more restrictive Windows Firewall policy to be applied to the external interface. This reduces the exposure of running services on the RRAS server to untrusted networks. This is especially critical if the VPN server is Windows Server RRAS and it is joined to a domain.

Network Performance

For very busy RRAS servers, having two network interfaces can improve network performance. With two network interfaces, network traffic is distributed between two network adapters, reducing utilization on each interface.

Dual NIC Best Practices

When deploying an RRAS server with dual NICs, the following recommendations for network interface configuration should be followed.

IP Addressing

Each network interface must be assigned an IP address from a unique subnet. Having both NICs on the same subnet is not supported.

Default Gateway

The default gateway should be configured on the external facing network interface only. The internal interface should not be configured with a gateway. Rather, static routes to any remote internal networks should be configured.

To add a static route on a Windows Server, open an elevated PowerShell command window and run the following command.

DNS

For domain-joined RRAS servers, corporate DNS servers should be configured on the Internal network interface only. No DNS servers should be configured on the external interface. If the server is not joined to a domain, DNS servers can be configured on whichever interface has connectivity to the defined DNS servers.

NAT

When the RRAS server is behind a device performing Network Address Translation (NAT), the NAT should be configured to translate only the destination address (DNAT). This allows the VPN server (or load balancer for multiserver deployments) to see the client’s original source IP address, which ensures efficient traffic distribution and meaningful log data.

Client, Service, and Protocol Bindings

All unnecessary clients, services, and protocols should be unbound from the external network interface. It is recommended that only the IPv4 and IPv6 protocols be enabled on the external interface, as shown here. Again, this reduces exposure for the server to the untrusted external network.

Summary

The dual NIC, multihomed configuration is generally recommended for most deployments as it offers security and performance advantages over the single NIC configuration. For organizations with less demanding security requirements, a single NIC deployment can be deployed safely without compromising functionality or supportability. In addition, a single NIC deployment may be the best option when multiple networks aren’t readily available.

When configuring Always On VPN, administrators have the option to enable DNS registration for VPN clients. When this option is set, VPN clients will register the IP address assigned to their VPN interface in the internal DNS. This allows client devices to be managed using their hostname from the internal network whenever they are connected remotely.

DNS Registration

DNS registration is enabled in one of two ways, depending on how Always On VPN client devices are managed.

Intune

When using the native Microsoft Intune UI to manage Always On VPN profiles, DNS registration can be configured by selecting Enabled next to Register IP addresses with internal DNS in the Base VPN settings section.

ProfileXML

When using custom ProfileXML with PowerShell, SCCM, or Intune, the administrator will define the RegisterDNS element to enable DNS registration.

Known Issues

Some users have reported unexpected behavior when DNS registration is enabled. Specifically, under some circumstances the VPN client will register the IP address of the VPN network interface along with the IP address of its public network interface (Wi-Fi, Ethernet, etc.). However, the VPN client can only be managed using the VPN interface. If the VPN client’s hostname resolves to its public IP address, manage out will fail.

This appears to happen only when Name Resolution Policy Table (NRPT) rules are defined in Intune DNS settings, or if the DomainNameInformation element is defined in ProfileXML.

Resolution

Microsoft recently released fixes for this DNS registration issue for Windows 10. The fix for this issue is included in the following updates.

Once complete, restart the client device for the changes to take effect. After validation testing is complete, the registry entry can be deployed to Always On VPN clients using Active Directory group policy preferences or Intune.

Windows Server and the Routing and Remote Access Service (RRAS) is a popular choice for Windows 10 Always On VPN deployments. It is easy to implement and support, offers flexible scalability, and is cost-effective. In addition, it provides support for a TLS-based VPN protocol which is required for many deployments.

Configuration Backup

When deploying RRAS to support Always On VPN, it’s an excellent idea to export the configuration once all settings have been finalized. Often this is done by opening an elevated command window and running netsh.exe ras dump and piping the output to a text file, as shown here.

netsh.exe ras dump > rasconfig.txt

Import Error

Importing a saved configuration is accomplished by opening an elevated command window and running netsh.exe exec [filename], as shown here.

netsh.exe exec rasconfig.txt

Oddly, this doesn’t work by default. The import will fail and return the following error message.

“The following command was not found: ■.”

Root Cause

Importing the RRAS configuration fails because the default configuration output is saved in Unicode format. Inexplicably this encoding is not recognized by netsh.exe when importing the configuration.

Workaround

Follow the steps below to save the configuration file in a format that can be imported using netsh.exe.

Once complete, import the file using netsh.exe exec [filename]. Restart the RemoteAccess service to apply the changes.

PowerShell

Administrators can use PowerShell to export the RRAS configuration and ensure the correct encoding format is used by default. To do this, open an elevated PowerShell window and run the following command.

When deploying Windows 10 Always On VPN using Microsoft Intune, administrators have two choices for configuring VPN profiles. They can use the native Intune user interface (UI) or create and upload a custom ProfileXML. The method chosen will depend on which features and settings are required.

Microsoft Intune

Intune has an intuitive user interface (UI) that can be used to configure and deploy Always On VPN profiles to Windows 10 clients. Guidance for using the UI to deploy Windows 10 Always On VPN with Microsoft Intune can be found here. However, Intune does not expose all Always On VPN settings to the administrator, which can be problematic.

Missing from Intune

At the time of this writing, the following Always On VPN settings cannot be configured natively using the Intune UI.

To implement any of the above features or settings the administrator must create and upload a custom ProfileXML.

ProfileXML

ProfileXML is a node within the VPNv2 Configuration Service Provider (CSP). When configuring Always On VPN using the Intune UI, each setting is configured individually. By contrast, the ProfileXML node includes all Always On VPN settings in a single configuration file. It can be deployed using Intune or PowerShell. Sample ProfileXML files for both user and device tunnels can be downloaded from my GitHub repository.

Custom OMA-URI Settings

1. In the Custom OMA-URI Settings blade click Add.
2. Enter a descriptive name in the Name field (this name will appear in the Windows UI on the client).
3. Enter ./User/Vendor/MSFT/VPNv2/Always%20On%20VPN/ProfileXML in the OMA-URI field. I’ve used Always On VPN as an example here, but you can use any text you like. If it includes spaces they must be escaped using %20, as shown here. Also, don’t forget to include the leading “.“.
4. Select String (XML file) from the Data type drop-down list.
5. Click the folder next to the Select a file field and select your ProfileXML file.
6. Click Ok.

Important Note: The File contents window must show the contents of your ProfileXML. If the contents are unreadable the XML file contains encoding that will not work. If this happens, copy the contents of your ProfileXML to another new text file and upload again.

Assign Profile

Follow the steps below to assign the Always On VPN profile to the appropriate user group.

Demonstration Video

A demonstration video with guidance for deploying a Windows 10 Always On VPN user tunnel using the native Microsoft Intune UI as well as custom ProfileXML can be found here. The custom ProfileXML guidance starts at 7:52.

The Windows Server Routing and Remote Access Service (RRAS) includes support for the Secure Socket Tunneling Protocol (SSTP), which is a Microsoft proprietary VPN protocol that uses SSL/TLS for security and privacy of VPN connections. The advantages of using SSTP for Always On VPN is that it is firewall friendly and ensures consistent remove connectivity even behind highly restrictive firewalls.

Load Balancing SSTP

In a recent post, I described some of the use cases and benefits of SSTP load balancing as well as the offloading of TLS for SSTP VPN connections. Using a load balancer for SSTP VPN connections increases scalability, and offloading TLS for SSTP reduces resource utilization and improves performance for VPN connections. There are positive security benefits too.

Configuration

Enabling load balancing on the Kemp LoadMaster platform is fundamentally similar to load balancing HTTPS web servers. However, there are a few subtle but important differences.

Health Check

Using a standard TCP port check on the LoadMaster will not accurately reflect the health of the SSTP service running on the RRAS server. In addition, using a simple TCP port check could yield unexpected results. To ensure accurate service status monitoring, it is recommended that HTTP or HTTPS health checks be configured instead.

Real Server Check Method

Open the Kemp LoadMaster management console and follow the steps below to enable HTTP/HTTPS health checks for SSTP.

TLS Offload

It is generally recommended that TLS offload not be enabled for SSTP VPN. However, if TLS offload is desired, it is configured in much the same way as a common HTTPS web server. Specific guidance for enabling TLS offload on the Kemp LoadMaster load balancer can be found in the Always On VPN Load Balancing Deployment Guide for Kemp Load Balancers. Details for configuring RRAS and SSTP to support TLS offload can be found here.

Certificates

When enabling TLS offload for SSTP VPN connections it is recommended that the public SSL certificate be installed on the RRAS server, even though TLS processing will be handled on the LoadMaster and HTTP will be used between the LoadMaster and the RRAS server. If installing the public SSL certificate on the RRAS server is not an option, additional configuration will be required. Specifically, TLS offload for SSTP must be configured using the Enable-SSTPOffload PowerShell script, which can be found here.

Once the script has been downloaded, open an elevated PowerShell command window and enter the following command.

Re-Encryption

When offloading TLS for SSTP VPN connections, all traffic between the LoadMaster and the RRAS server will be sent in the clear using HTTP. In some instances, TLS offload is required only for traffic inspection, not performance gain. In this scenario the LoadMaster will be configured to terminate and then re-encrypt connections to the RRAS server. When terminating TLS on the LoadMaster and re-encrypting connections to the RRAS server is required, the same certificate must be used on both the LoadMaster and the RRAS server. Using different certificates on the RRAS server and the load balancer is not supported.

After deploying or upgrading to Windows 10 1903, administrators may find that Windows 10 Always On VPN connections fail to establish successfully. Always On VPN connections continue to work for Windows 10 1809 and earlier clients, however.

Important Note: The issue described in this article has been addressed in KB4505903 (build 18362.267) released July 26, 2019.

RasMan Event Log Errors

When this occurs, the application event log contains an error with Event ID 1000 that includes the following information.

Organizations everywhere are rapidly adopting Microsoft Azure public cloud infrastructure to extend or replace their existing datacenter. As traditional on-premises workloads are migrated to the cloud, customers are looking for options to host VPN services there as well.

Windows Server

Windows Server with the Routing and Remote Access Service (RRAS) installed is a popular choice for on-premises Always On VPN deployments. Intuitively it would make sense to deploy Windows Server and RRAS in Azure as well. However, at the time of this writing, RRAS is not a supported workload on Windows Server in Azure.

Although explicitly unsupported, it is possible to deploy Windows Server and RRAS in Azure for Always On VPN. In my experience it works well and can be an option for organizations willing to forgo formal support by Microsoft.

Azure Gateway

Options for supporting Always On VPN connections using native Azure VPN infrastructure depend on the type of VPN gateway chosen.

VPN Gateway

The Azure VPN Gateway can be configured to support client-based (point-to-site) VPN. With some additional configuration it can be used to support Windows 10 Always On VPN deployments. Azure VPN gateway supports both IKEv2 and SSTP VPN protocols for client connections. The Azure VPN gateway has some limitations though. Consider the following:

A route-based VPN gateway is required

A maximum of 1000 concurrent IKEv2 connections are supported when using the VpnGw3 or VpnGw3AZ SKUs (2000 supported in active/active mode)

A maximum of 128 concurrent SSTP connections are supported on all gateway SKUs (256 supported in active/active mode)

Virtual WAN

Azure Virtual WAN is the future of remote connectivity for Azure. It includes support for client-based VPN (currently in public preview at the time of this writing), but only supports IKEv2 and OpenVPN VPN protocols for client connections. SSTP is not supported at all. Further, OpenVPN is not supported for Windows 10 Always On VPN, leaving IKEv2 as the only option, which poses some potential operational challenges. Virtual WAN offer much better scalability though, supporting up to 10,000 concurrent client-based VPN connections.

Virtual Appliance

The most supportable option for hosting VPN services in Azure for Windows 10 Always On VPN is to deploy a third-party Network Virtual Appliance (NVA). They are available from a variety of vendors including Cisco, Check Point, Palo Alto Networks, Fortinet, and many others. To support Windows 10 Always On VPN, the NVA vendor must either support IKEv2 for client-based VPN connections or have a Universal Windows Platform (UWP) VPN plug-in client available from the Microsoft store. Click here to learn more about Always On VPN and third-party VPN devices.

Note: Be careful when choosing an NVA as some vendors support IKEv2 only for site-to-site VPN, but not client-based VPN!

Hybrid Deployments

For organizations with hybrid cloud deployments (infrastructure hosted on-premises and in Azure), there are several options for choosing the best location to deploy VPN services. In general, it is recommended that client VPN connections be established nearest the resources accessed by remote clients. However, having VPN servers hosted both on-premises and in Azure is fully supported. In this scenario Azure Traffic Manager can be configured to intelligently route VPN connections for remote clients.

NetMotion Mobility

The NetMotion Mobility purpose-built enterprise VPN is a popular replacement for Microsoft DirectAccess. It is also an excellent alternative for enterprise organizations considering a migration to Always On VPN. It is a software-based solution that can be deployed on Windows Server and is fully supported running in Microsoft Azure. It offers many advanced features and capabilities not included in other remote access solutions.

Summary

Administrators have many options for deploying VPN servers in Azure to support Windows 10 Always On VPN. Windows Server and RRAS is the simplest and most cost-effective option, but it is not formally supported by Microsoft. Azure VPN gateway is an interesting alternative but lacks enough capacity for larger deployments. Azure Virtual WAN is another option but has limited protocol support. Deploying an NVA is a good choice, and NetMotion Mobility is an excellent alternative to both DirectAccess and Always On VPN that is software-based and fully supported in Azure.

Recently I wrote about denying access to Windows 10 Always On VPN users or computers. In that post I provided specific guidance for denying access to computers configured with the device tunnel. To summarize, the process involved exporting the device certificate from the issuing Certification Authority (CA) server and placing it in the Untrusted Certificates certificate store on each VPN server. In theory, simply revoking the device certificate should be all that’s required to prevent device tunnel connections.

Revocation Check Failure

As it turns out, a bug in Windows Server Routing and Remote Access prevents this from working as expected. Windows Server 2012 R2, 2016, and 2019 all fail to check the Certificate Revocation List (CRL) for IKEv2 VPN connections using machine certificate authentication (for example an Always On VPN device tunnel).

Update for Windows Server

Microsoft recently made a fix for this issue available for Windows Server 2016. It is included in the June 18, 2019 update KB4503294 (build 14393.3053). A fix for Windows Server 2019 is forthcoming. Windows Server 2012 R2 will not be updated. It is recommended that you upgrade to a later version of the Windows Server operating system to address this issue.

Note: This fix is now available for Windows Server 1903 (semi-annual channel). It is included in the June 27, 2019 update KB4501375 (build 18362.207).

Enable Revocation Check

Additional configuration is required to enable support for CRL checking. Microsoft published guidance for configuring CRL revocation checks for IKEv2 VPN connections using machine certificate authentication here. Specifically, administrators must enable the RootCertificateNameToAccept parameter and set a registry key to enable this functionality.

Open an elevated PowerShell window and run the following commands to enable CRL checking for IKEv2 VPN connections using machine certificate authentication.

A PowerShell script to update the RootCertificateNameToAccept parameter on multiple VPN servers can be found here.

Revoking Certificates

To prevent a Windows 10 Always On VPN device tunnel connection, the administrator must first revoke the certificate on the issuing CA. Next, open an elevated command window an enter the following commands. Repeat these steps on each VPN server in the enterprise.

The Windows Server Routing and Remote Access Service (RRAS) includes support for the Secure Sockets Tunneling Protocol (SSTP), which is a Microsoft proprietary VPN protocol that uses SSL/TLS for security and privacy of VPN connections. The advantage of using SSTP for Always On VPN is that it is firewall friendly and ensures consistent remote connectivity even behind highly restrictive firewalls.

Load Balancing SSTP

In a recent post, I described some of the use cases and benefits of SSTP load balancing as well as the offloading of TLS for SSTP VPN connections. Using a load balancer for SSTP VPN connections increases scalability, and offloading TLS for SSTP reduces resource utilization and improves performance for VPN connections. There are positive security benefits too.

Configuration

Enabling load balancing for SSTP on the F5 BIG-IP platform is fundamentally similar to load balancing HTTPS web servers. However, there are a few subtle but important differences.

Default Monitor

The default HTTP and HTTPS monitors on the F5 will not accurately reflect the health of the SSTP service running on the RRAS server. In addition, using a simple TCP port monitor could yield unexpected results. To ensure accurate service status monitoring, a new custom monitor must be created to validate the health of the SSTP service.

Custom SSTP Monitor

Open the F5 BIG-IP management console and follow the steps below to create and assign a new custom monitor for SSTP.

Create Monitor

4. Enter a descriptive name in the Name field and from the Type drop-down list choose HTTP if TLS offload is enabled, or HTTPS if it is not.
5. In the Send String field enter HEAD /sra_{BA195980-CD49-458b-9E23-C84EE0ADCD75}/ HTTP/1.1\r\nHost:r\nConnection: Close\r\n\r\n.
6. In the Receive String field enter HTTP/1.1 401.
7. Click Finished.

Assign Monitor

1. Below Local Traffic click Pools.
2. Click on the SSTP VPN server pool.
3. In the Health Monitors section select the SSTP VPN health monitor from the Available list and make it Active.
4. Click Update.

CLI Configuration

If you prefer to configure the SSTP VPN monitor using the F5’s Command Line Interface (CLI), you can download the monitor configuration from my GitHub here.

TLS Offload

It is generally recommended that TLS offload not be enabled for SSTP VPN. However, if TLS offload is desired, it is configured in much the same way as a common HTTPS web server. Specific guidance for enabling TLS offload on the F5 BIG-IP can be found here. Details for configuring RRAS and SSTP to support TLS offload can be found here.

Certificates

When enabling TLS offload for SSTP VPN connections it is recommended that the public SSL certificate be installed on the RRAS server, even though TLS processing will be handled on the F5 and HTTP will be used between the F5 and the RRAS server. If installing the public SSL certificate on the RRAS server is not an option, additional configuration will be required. Specifically, TLS offload for SSTP must be configured using the Enable-SSTPOffload PowerShell script, which can be found here.

Once the script has been downloaded, open an elevated PowerShell command window and enter the following command.

Re-Encryption

When offloading TLS for SSTP VPN connections, all traffic between the F5 and the RRAS server will be sent in the clear using HTTP. In some instances, TLS offload is required only for traffic inspection, not performance gain. In this scenario the F5 will be configured to terminate and then re-encrypt connections to the RRAS server. When terminating TLS on the F5 and re-encrypting connections to the RRAS server is required, the same certificate must be used on both the F5 and the RRAS server. Using different certificates on the RRAS server and the load balancer is not supported.

When deploying Windows 10 Always On VPN using Protected Extensible Authentication Protocol (PEAP) authentication with client certificates, administrators may find the VPN connection does not establish automatically. In this specific scenario the client is prompted to select a certificate to use to authenticate to the VPN server.

Multiple Certificates

This can occur when certificates from multiple Certification Authorities (CAs) are issued to the user that include the Client Authentication Enhanced Key Usage (EKU). When this happens, the user is forced to select the correct certificate to use for VPN authentication.

Clearly this is less than ideal, as it not only breaks the seamless and transparent nature of Always On VPN, the user may select the wrong certificate resulting in authentication failure. Ideally the client should be configured to select the correct certificate without user interaction.

Select the root CA used to issue client authentication certificates for VPN authentication.

Click Ok four times to save the configuration.

Once complete, export the EAP configuration to XML from the VPN client and paste the new settings in Intune or in your custom ProfileXML.

Certificate Purpose

By default, a client certificate requires only the Client Authentication EKU to establish a VPN connection. In some cases, this may not be desirable. For example, consider a deployment where Client Authentication certificates are issued to all users for Wi-Fi authentication. Depending on the Network Policy Server (NPS) configuration, these certificates may also be used to authenticate to the VPN.

VPN Specific Certificate

Follow the steps below to create a user authentication certificate template to be used exclusively for VPN authentication.

Certificate Template

On the CA server, open the Certificate Templates management console (certtmpl.msc).